As an apparatus for producing a numerical control program for detecting the existence or non-existence of a groove-like turning sectional shape to which a turning-processing is to be performed from one-quarter sectional shape data, in which a plane containing the turning axis of a product shape model is set as a cross section, and turning-processing the detected turning sectional shape, conventionally, there is known an apparatus including a unit for determining the turning sectional shape to be a relief sectional shape in a case where the width and depth of the turning sectional shape are equal to or smaller than a predetermined relief parameter and the turning sectional shape exists in a perpendicular corner. Also an apparatus for producing a numerical control program for turning-processing a relief with a turning tool bit is known (see Patent Reference 1).
The relief is also called a clearance. The relief is a type of a groove shape which is provided to a part for various objects such as that parts becomes in close contact with each other without a gap therebetween, concentrated stress is relieved, and a portion that is not turning-processed is prevented from being formed at a corner (because the edge of a tool bit is rounded). A relief is processed by a turning tool bit such as shown in FIG. 3(a).